Which of the following has the most primitive respiratory system?
snail
fish
insect
mouse
Correct answer is A
The evolutionary trend of respiratory systems from simple to complex
Diffusion through skin/cell → gills → tracheal tubes → book lungs → lungs
Some groups of snails that live in freshwater respire with gills, while other groups need to reach the surface to breathe air. In addition, some are amphibious and have both gills and a lung. Their lack of organ specificity accounts for their primitive status when it comes to respiration.